JP2799147B2 - X-ray CT system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses a microfocus type X-ray TV apparatus (a device for displaying a fluoroscopic X-ray image) and examines a subject with a fluoroscopic image and also uses a tomographic image (X-ray CT image). The present invention relates to an X-ray CT apparatus capable of inspection.

[0002]

2. Description of the Related Art Conventionally, real-time inspection is possible for non-destructive inspection inside a subject such as a molded electronic component.
X-ray T for observing fluoroscopic images because of its simple operation
V devices are commonly used.

However, in the case of a subject having a complicated internal structure or a multi-layer structure, the above-mentioned perspective image (two-dimensional projection of a three-dimensional component) is inspected because a portion to be focused on overlaps with another component. Becomes difficult. For this reason, an inspection using an X-ray CT apparatus capable of nondestructively observing a tomographic image of a subject is required.

However, in the conventional X-ray CT apparatus, the X-ray generator, the X-ray detector, and the rotational axis of the subject are accurately positioned with the accuracy required for tomography, and the rotational motion of the subject does not occur. The rotating device is likely to be large-scale and expensive. That is, the conventional X
Since the X-ray TV apparatus is dedicated to a fluoroscopic image, the position of the rotation center axis of the subject does not always coincide with the center position of the X-ray detector, and the positioning accuracy of the subject mounting table is insufficient for tomography. In addition, the rotating device is configured to easily cause rotational blur due to the size, shape, and gripping mechanism of the subject. In particular, positioning of the rotation axis of the subject is important.
Therefore, in order to perform tomography using a conventional X-ray TV apparatus, it is necessary to replace the subject mounting table, the gripping mechanism, and the rotating device with those dedicated to CT, which is inconvenient in that the operation is inconvenient. Was seen.

An X-ray CT apparatus has been proposed which detects the center axis of rotation of the subject from the contour position of the fluoroscopic image and enables tomography without performing advanced positioning of the subject. (Japanese Patent Application No. 04-289460). According to this proposal, the coordinate value (X coordinate) of the rotation center axis in the X-ray detector is represented by Xs, the projection data coordinate value when the subject has reached the minimum value of the X coordinate, and the subject has the maximum X coordinate. Assuming that the coordinate value of the projection data when reaching the value is Xm, the true rotation center axis can be obtained by ((Xs + Xm) / 2). Then, reconstruction processing can be executed from projection data of a required number of samples. However, this formula can be used when the X-ray beam can be approximated as a parallel beam, or when the fan-shaped radiation beam projection, each detecting element of the X-ray detector is arranged at the same distance from the X-ray source focal point. Limited to

On the other hand, in recent years, a microfocus type, so-called microfocus type X-ray TV apparatus has become the mainstream of industrial X-ray TV apparatuses in order to improve the resolution of a fluoroscopic image of a subject. The X-ray beam of the microfocus type X-ray TV device is radiated in a fan shape, and the detection surface of the X-ray detector is planar. In addition, other X-ray TV apparatuses often have the same configuration using a fan-shaped radiation beam. Therefore, if the detection surface of the X-ray detector is planar in such a fan-shaped radiation beam projection, the true rotation center axis cannot be obtained by the positioning using the above formula, and a new calculation formula is constructed. There is a need to.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to utilize both a fluoroscopic image and a CT image by the above-mentioned micro-focus X-ray TV apparatus or other X-ray CT apparatus using a fan-shaped radiation beam. An object of the present invention is to provide an X-ray CT apparatus which does not require positioning of a true rotation center axis of a subject without changing its basic configuration.

[0008]

According to the present invention, in order to achieve the above object, an X-ray generator and an X-ray detector are arranged opposite to each other with a subject interposed therebetween. Means for processing an X-ray image transmitted through the X-ray CT and means for detecting the contour position of the subject in each direction from the density information of the X-ray image obtained by the image processing means.
In the apparatus, an X-ray projection connecting the focal point of the X-ray source and the rotation center position is provided.
The radiation center line connects the X-ray source focal point and the predetermined center position of the X-ray detector.
Angle does not match the predetermined center line
When the projection is performed obliquely to the X-ray detector detection surface
Means for detecting the deviation angle from the contour position of the subject even if
And rotation of the subject in the X-ray detector from the deviation angle
A means for detecting the center axis projected position is provided, and
An object of the present invention is to calculate a projection position of a subject necessary for reconstruction, and to enable tomography without performing advanced positioning of the subject.

[0009]

The present invention will be described with reference to the drawings. As shown in FIG. 1, assuming that the X coordinate minimum value and the maximum value on the perspective image of the object contour projection data obtained by rotating the object by one rotation are Xs and Xm, respectively, a predetermined center position (Xc) of the X-ray detector. ) And α2, respectively. It is. Here, LEN1 is the actual distance from the X-ray source focal point to the X-ray detector, and LEN2 is １ ／ of the actual distance at which the X-ray detector detects X-rays.

The spread angle (2 × β) of the X-ray beam is: 2 × β = α1 + α2 (3) The deviation angle of the rotation center position O from the X-ray detector center position is γ = α2-β = (α2- α1) / 2 (4).

FIG. 2 shows a normalized coordinate axis V of the detector used in the conventional fan-shaped beam projection (the center of rotation and the center of the X-ray detector coincide with each other), and the center of rotation is the center of the X-ray detector. A coordinate axis W when the positions do not match (oblique projection to the X-ray detector) is shown. Here, the rotation center position in the X-ray detector is determined by obtaining distances x and y on the coordinate axis W.

From the sine theorem It is. Therefore, the rotation center position coordinate Xo is It is.

In the case where a beam that has passed through the rotation center position from the X-ray source focal point is vertically incident on the detection surface of the X-ray detector (projection in which the conventional rotation center position and the X-ray detector center position match), The necessary projection data is represented by a value p normalized on the coordinate axis V. On the other hand, in the oblique fan beam projection, the detection plane is the coordinate axis W, and in this case, reconstruction from the fan beam projection requires conversion from p on the coordinate axis V to z on W.

This conversion is performed by the following calculation. 1) For -1 ≦ p ≦ 0 From the sine theorem It is.

Similarly, 2) When 0 ≦ p ≦ 1 It is.

Thus, C in the oblique fan beam projection is obtained.
X-ray projection data on the X-ray detector required for T image reconstruction can be specified. The above calculation is an example of α2> α1, but the same applies to the case of α2 <α1.

[0017]

An embodiment of the present invention will be described with reference to the drawings.
As shown in FIG. 3, a fan-shaped radiation beam X-ray T comprising an X-ray generator 2, an X-ray detector 3 for detecting a fluoroscopic image of the subject P, and the like.
A rotation control device 4 that controls the rotation of the gripping mechanism of the subject P in the V device 1, executes a process of image input, and executes a fluoroscopic image and CT.
An image input / processing device 5 having an image display CRT 6 for displaying a reconstructed image for use, and a personal computer 7 for executing control of the device, image reconstruction processing, and the like.

The personal computer includes control units such as a contour detection device 8 for the subject P, a rotation center axis detection / coordinate axis conversion device 9 for the subject P, and a tomographic image reconstruction processing device 10. Also, the gripping mechanism of the subject utilizes an electronic component grip.

The rotation control device 4 generates a rotation output signal of the subject P by a rotation input signal from the personal computer 7 so that projection data of the subject P can be collected from all directions of 360 degrees. There is a step angle rotation mode. The continuous rotation mode is for setting the position of the subject P and setting the X-ray output, and the rotation angle step is set to 1 degree, 2 degrees, or the like.

Next, the operation of each device at the time of CT image observation will be described with reference to the flowchart shown in FIG.

Since the optimum value of the intensity of the incident X-ray varies depending on the amount of X-ray absorbed by the subject P, the X-ray output is set to the optimum value from the fluoroscopic information (step (1)).

The input conditions of the projection data are set. The input conditions include a rotation angle step required for the perspective image of the projection image, the number of projection directions, the number of integration of the perspective image, and the like (step (2)).

The rotation of the subject P is executed (steps (3) and (4)), and the image quality of the fluoroscopic image caused by random noise of the X-ray detector 3 is compensated for by image integration of 5 to 30 times (step (3)). 5)), and store the projection data with the improved SN ratio (step (6)).

For projection data necessary for CT, a fluoroscopic image is converted into an 8-bit digital value, and its input and basic preprocessing are performed by an image input / processing device 5.

Since the same subject has a different density level depending on its structure and site / direction, the subject contour detecting device 8
The density of the input image is measured for each direction, the contour position of the subject is detected, the deviation angle is detected from equation (4), and the rotation center axis position is determined by the rotation center axis detection device 9 (step (7)). ), Necessary projection data of the subject P is obtained by coordinate transformation (step (8)), and reconstruction processing is performed (step (9)).

If there is no means for accurately positioning the subject and the rotation axis with respect to the position of the X-ray detector 3, the contour position of the subject differs depending on the setting of the subject, but the projected image of the subject always enters the fluoroscopic image. With this setting, it is possible to detect the rotation operation of the subject center position due to the rotation blur.

Then, the true rotation center axis Xo is given by the following equation (1).
It is determined according to (7). Also, the projection data sample positions required for reconstruction from the oblique fan-shaped X-ray beam projection are calculated from equations (8) and (9).

In the tomographic image reconstruction processing apparatus 10, the expression (8)
Reconstructing a tomographic image by filter-corrected backprojection processing using the projection data sample values obtained in step (9),
Observation is made on the image display CRT 6 and stored (step (10)).

The reconstruction processing of the object contour detection device 8, the rotation center axis detection device 9, the tomographic image reconstruction processing device 10 and the like is executed by software on a personal computer.

[0030]

The present invention utilizes a perspective image of a microfocal type fan-shaped radiation beam X-ray TV apparatus, and does not require the positioning accuracy of the subject, and automatically rotates and rotates the X-ray image from the X-ray image. Since the tomographic image is captured by detecting the axis, the CT inspection can be performed at a low cost without introducing a new dedicated CT apparatus.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration outline of the present invention.

FIG. 2 is a flowchart showing an operation.

FIG. 3 is an explanatory diagram of detection of a rotation center axis of a subject.

FIG. 4 is a diagram illustrating coordinate conversion of projection data of oblique projection.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 X-ray TV device 2 X-ray generator 3 X-ray detector 4 Rotation control device 5 Image input / processing device 6 Image display CRT 7 Personal computer 8 Subject outline detection device 9 Rotation center axis detection device 10 Tomographic image reconstruction processing apparatus

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-118030 (JP, A) JP-A-61-181443 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01N 23/04-23/18 A61B 6/00-6/14

Claims (1)

(57) [Claims] 1. An X-ray generator in which an X-ray generator and an X-ray detector in which a detection element is arranged in a straight line or in a plane across a subject are opposed to each other. an image processing unit of the line image, the X-ray CT apparatus according to fan radiation beam having a means for detecting the contour position of the object in each direction from the density information of the X-ray image obtained by the image processing means, the X-ray source focal point X-ray projection center line connecting the rotation center position with
Is between the focal point of the X-ray source and the predetermined center position of the X-ray detector
Does not match the core wire, has a deviation angle with respect to the predetermined center line,
Even in the case of oblique projection to the X-ray detector detection surface,
Means for detecting the angle of deviation from the contour position of the subject,
Projection of rotation center axis of subject on X-ray detector from angle
Equipped with a means for detecting the position, for reconstruction by coordinate axis transformation
An X-ray CT apparatus compatible with a fan-shaped radiation beam X-ray TV apparatus , which calculates a required subject projection position and enables tomography without performing advanced positioning of the subject.